Toners are used for the development of electrophotographic images and in a variety of electrostatic printing and copying apparatuses. Toners refer to coating substances that can be transferred and fixed to objects to form desired patterns thereon. As computer-aided documentation has been generalized in recent years, there has been a rapidly increasing demand for imaging apparatuses, such as printers. In response to this demand, the use of toners is also on the rise.
Methods for the production of toners are largely classified into two types of methods based on pulverization and polymerization. The first type of methods based on pulverization is most widely known. According to a typical method based on pulverization, a resin and a pigment is melt-mixed or extruded, pulverized and sorted on the basis of size to obtain toner particles. However, the toner particles have a broad particle diameter distribution and are very irregular in shape (e.g., sharp edges), which are disadvantageous in terms of charge properties and flowability.
To overcome the above disadvantages of the first type of methods, the second type of methods based on polymerization for the production of spherical toner particles has been proposed. It is known that the second type of methods can be carried out by emulsion polymerization/aggregation and suspension polymerization. According to emulsion polymerization, however, the size distribution of particles is difficult to control and the reproducibility of toner quality remains problematic. For these reasons, suspension polymerization is predominantly employed in preference to emulsion polymerization.
However, toner particles produced by suspension polymerization also have a broad size distribution, which necessitates an additional separation step. Further, a toner having undergone size separation is consumed in a large amount during printing and is unsatisfactory in terms of transferability.